1. Field of the Invention
This invention pertains to a process for recovering viscous petroleum from a subterranean, viscous petroleum-containing formation. More particularly, this invention is concerned with a particular method for injecting steam into a subterranean viscous petroleum-containing formation by a single well push-pull method in which steam injection and oil production occurs in the same well using a pressure pulsing technique to stimulate production at greater distances in the formation.
2. Description of the Prior Art
Many petroleum reservoirs have been discovered which contain vast quanities of petroleum, but little or no petroleum has been recovered from many of them because the petroleum present in these reservoirs is so viscous that it is essentially immobile at reservoir conditions, and little or no petroleum flow will occur into a well drilled into the formation even if a natural or artificially induced pressure differential exists between the formation and the well. Recovery of such viscous oil can sometimes be accomplished by solvent means, but the cost of solvent flooding is usually excessive in relation to the petroleum production obtainable thereby. Thermal stimulation has been effective in some formations, and generally involves injecting steam into one or more wells and taking production of petroleum heated by the steam from the same or a remotely located well.
Throughput steam injection is more efficient for recovering viscous oil, but usually cannot be applied initially to low permeability formations and many viscous oil formations are not sufficiently permeable to permit steam throughput. Single well bore stimulation by so called steam push-pull processes in which steam is injected into a formation, allowed to remain in contact with the formation for a soak period sufficient to heat the viscous petroleum and reduce its viscosity, followed by reduction in well bore pressure sufficient to cause the heated petroleum to flow back into the well, has been successful in some applications. Problems encountered in push-pull steam stimulation generally are related to the limited penetration of the steam into the formation, with the result that the amount of oil heated sufficiently to permit its recovery from the formation is insufficient to justify the cost of the steam injected into the formation. Injecting higher quality steam, up to and including superheated steam can achieve stimulation of oil production at greater distances from the well, but the cost of generating superheated steam is excessive and other problems are encountered in the use of high quality steam including higher injection pressures per heat unit injected and excessive casing failures.
In view of the above discussed problem and the fact that large quantities of viscous petroleum are known to exist in this country from which little production is being obtained at the present time, and in view of the current urgency to increase our domestic oil production capacity, it can be appreciated that there is a substantial need for a means of operating a single well, push-pull steam stimulation process in a manner which achieves greater in depth stimulation and recovers oil from a large portion of the formation that is currently possible with conventional single well, push-pull steam stimulation techniques.